Numerous apparatus have been developed for drying wet sludgelike materials, such as metal hydroxide sludge as generated in plating operations and the like. Such apparatus, of both the batch and continuous type, often employ heaters and/or agitators to reduce the drying time as a heating fluid, normally air, is circulated therethrough. While these known apparatus have operated in a reasonably satisfactory manner, nevertheless there is an ongoing need for improvements in such drying apparatus which improve operational efficiency and reduce operating costs, and/or increase the amount of moisture which can be efficiently removed from the sludgelike material.
In one known apparatus, as disclosed in German Gebrauchsmuster No. G9100341.5, the sludge drying apparatus is of the batch-type and utilizes a closable boxlike housing in which a wheeled hopper containing a batch of sludge can be positioned. The housing contains a refrigeration-type air drying apparatus which defines a closed recirculating air system for supplying dry air into the bottom of the hopper so that the air is fed upwardly through the sludge to remove moisture therefrom, with the wet air being dried and then resupplied to the drying apparatus for removing moisture therefrom. The air is contained in a closed recirculating system while permitting reasonably efficient removal of moisture therefrom, and hence removal of moisture from the sludge to permit drying thereof.
In the aforementioned apparatus, however, numerous structural and operational features are present which make both construction and use of this apparatus less than optimum. For example, the hopper has an operable front door to assist in removing the dried material when the hopper is removed from the apparatus, although it has been discovered that unloading of the material nevertheless still often requires manual shoveling of the material from the drying chamber for discharge through the front door. Further, in this known apparatus some of the dried material tends to fall through the perforated floor plate into the air supply chamber, and such material can be removed from the air supply chamber only by manually removing it through the air supply opening as formed in the back wall of the hopper. This known apparatus also lacks adequate controls for safe and automatic operation of the apparatus, and for example requires that the drying apparatus be defrosted by means of a manually-controlled switch.
Accordingly, it is an object of this invention to provide an improved batch-type drier, particularly for drying sludge such as filter cake, which improved drier overcomes many of the disadvantages associated with the drier described above.
More specifically, the improved drier includes a boxlike housing for receiving a hopper therein which contains a batch of wet sludge. The hopper cooperates with the housing, when closed therein, to define a closed air recirculation system which supplies dry pressurized warm air into a small air-receiving chamber located at the bottom of the hopper. The air passes upwardly through a perforated bottom wall into and through the sludge to remove moisture therefrom. The moist air passes upwardly through the open top of the hopper, through a filter and is supplied to a drying unit located in the housing for removing moisture therefrom, which moisture is externally discharged. The drying unit resupplies the dry air back to the drying chamber formed in the hopper. The air remains captivated and is recirculated to prevent escape of undesired volatiles, but significant moisture is nevertheless removed and externally discharged so as to permit efficient drying of the sludge without use of a separate heater.
In this improved drier, the sludge is deposited in the hopper through the upper top thereof, and is also discharge therefrom by tipping of the hopper after the sludge has been dried. For this purpose, the hopper has supporting structure associated with the bottom thereof for accommodating the tines or lifting elements of a conventional forklift truck. The supporting structure is normally rigidly coupled to the bottom of the hopper through a releasable latch. This supporting structure, when unlatched, permits relative vertical tilting of the hopper with respect to the supporting structure, which tilting is constrained to a limited angular extent by a restraining structure associated with the supporting structure. This arrangement enables the hopper containing the dried material to be attached to the lift fork and raised upwardly and then tilted over a receiving container so that the dried material can be dumped from the hopper through a discharge opening in the back wall thereof. This simultaneously permits any dried material which has fallen into the drying chamber to move toward and be discharged outwardly through the air supply opening so as to permit dumping of material from the drying chamber automatically and simultaneous with dumping of the material from the main drying chamber.
In this improved drier, as aforesaid, the perforated bottom wall of the drying chamber can be generally flat and spaced only a small distance from the bottom wall of the air supply chamber, thereby maximizing the capacity of the sludge-receiving drying chamber.
The improved drier, as aforesaid, also incorporates automatic controls which permit actuation of the overall apparatus only when the hopper is properly positioned and latched within the housing and the doors closed so as to then permit operation of the air recirculation and drying system. The drying system also incorporates an automatic defrost cycle and sensor which automatically initiates defrosting when such is required to hence optimize efficient operation of the system.
The improved drier, as aforesaid, also incorporates improvements in the air drying system to optimize the condensation of moisture from the air after passing through the hopper, and the efficient operation of the refrigeration part of the drying system.
Other desirable structural and operational features of the present invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.